Each year, over 60 million surgical procedures are performed in the United States. While great care is taken to prevent surgical complications, one overlooked and under-addressed problem is the risk of developing hypothermia before, during or after surgery (referred to as “inadvertent perioperative hypothermia” or “IPH”). Patient temperatures can drop precipitously during surgery, due to the effects of general anesthesia, lack of insulating clothing, and exposure to cold operating room temperatures. Even with today's standard of care, 30-50% of surgical patients will develop hypothermia.
Hypothermia often causes much more than patient discomfort. Patients who suffer even mild hypothermia are at significantly elevated risk for developing surgical site infections, cardiac morbidities, and other complications. Together, these significantly increase recovery time and overall length of hospital stay, leading to increased costs for all parties. By some estimates, unmanaged risk for IPH is a $15 billion problem in the United States alone, and yet is largely overlooked.
Perioperative heat loss occurs predominantly via convective heat transfer, particularly through the palms of the hands and soles of the feet. During preoperative care, patients are dressed solely in a gown and are often exposed to cold waiting areas with little insulation. Therefore, although patients are only anesthetized during surgery, patients often arrive to the surgical theater already slightly hypothermic. This puts a patient under greater risk for developing hypothermia once anesthesia has been administered. Postoperative drops in core temperature increase the likelihood of developing additional morbidities, such as morbid cardiac outcomes, surgical site infections, and blood loss, any of which typically prolongs recovery and hospitalization.
Patients undergoing surgery are very likely to develop hypothermia during the surgical procedure itself, especially when the procedure involves their core area, such as procedures involving the thoracic, abdominal, and pelvic regions. Surgeries of the core involve the exposure of vital internal organs to the cooler environment and thus carry a greater risk of hypothermia. Furthermore, core surgeries often necessitate the uncovering of the trunk and chest, which render blankets and many other existing interventions inadequate. Once in the operating room, patients are naked and exposed to a room temperature well below 36 degrees Celsius and to cold liquids used to wash the surgical site during sterilization preparation. At the onset of surgery, delivered anesthetics immediately impair the normal autonomic thermoregulatory controls. Colder blood is transferred from the peripheries of the body to the core through a phenomenon known as redistributive hypothermia. Vasodilatation and reduction in muscle tone cause a significant drop in core temperature within the first half-hour of surgery.
The development of IPH is strongly correlated with a multitude of physiological organ system changes, impacting the cardiovascular, respiratory, neurologic, immunologic, hematologic, drug metabolic, and wound healing mechanisms. The incidence of several post-surgical complications is increased due to even mild hypothermia. Intraoperatively, hypothermia can cause a decrease in cardiac output and heart rate, which can lead to ventricular dysrhythmias. Platelet functions become impaired and there is a decrease in coagulation factors, which leads to greater intraoperative bleeding and blood loss. Impaired immune functions increase the rate of surgical site infections. Hypothermia is associated with a four-fold increase in surgical would infection and twice as many morbid cardiac events. These complications and others are supported in multiple studies and result in both clinical and economic burdens.
Overall, compared to non-hypothermic patients, those who suffer IPH experience greater rates of surgical site infections, bleeding, cardiac complications which may require additional monitoring, PACU length of stay, total length of stay, and subjective discomfort. Although it is counterintuitive, the likelihood of developing hypothermia in an open versus laparoscopic surgery is similar across various types of procedures, most likely attributable to the fact that most laparoscopic procedures are significantly longer when compared to their open surgery counterpart.
Current methods of preventing hypothermia are not completely effective. Even with the current interventions, up to 46% of patients are reported to be hypothermic at the start of surgery and 33% are hypothermic upon arrival to the PACU. Assuming the cost savings for maintaining normothermia in one patient is approximately $5,000 per patient, and approximately 30% of the 17 million high-risk surgical patients are hypothermic, a system-wide cost savings of $15 billion will be realized by keeping these patients normothermic. With rising healthcare costs and recent initiatives by CMS mandating the maintenance of perioperative normothermia, hospital administrators nationally are in need of new, efficacious and cost-effective devices to address perioperative hypothermia, a product space which has seen little innovation since the introduction of the forced air warming blanket nearly three decades ago.
Currently available devices for perioperative warming are primarily forced air warming blankets. In particular, the Bair Hugger™ device (Arizant Healthcare, Inc.) is the most commonly used technology and is used in 85% of U.S. hospitals. Newer alternatives include high-heat transfer conduction heating blankets and intraoperative hand warming devices. Although these devices are somewhat effective, they all have several key shortcomings: (1) They are cumbersome, and thus compliance and correct usage is low; (2) Warming in the intraoperative period alone is significantly less effective than warming preoperatively and intraoperatively; and (3) Devices that heat via the core of body are ineffective during surgeries of that anatomical area. Currently available devices are often not used or not practical for use in preoperative warming for one or more of the following reasons: (1) They immobilize the upper limbs; (2) They are cumbersome—e.g., they float on the patient and get blown off during implementation and transport and they require large, predominantly floor-based blowers that are not mobile; (3) They are not attached to the patient and become dislodged during transport and obstruct the bed and other monitors and devices; and/or (4) They require a conscious administrative decision to implement. This has been shown to take up to 30 minutes to deploy effectively in clinical studies. A busy and stressed preoperative nurse cannot afford this time.
Additionally, currently available patient warming devices are often not used for any of the above reasons and/or any of the following reasons: (1) Fear of contaminating surgical field—e.g., forced air methods can blow bacteria containing air onto the surgical field; (2) Forced air blankets get in the way—e.g., to warm the core, they need to be in contact with the core; and/or (3) Operating room staff may turn down the temperature on the device due to their own comfort—e.g., operating room staff turns down the patient's forced air due to air escape heating the surrounding staff.
Therefore, it would be advantageous to have improved methods and systems for maintaining a patient's core body temperature before, during and/or after surgery. Ideally, such methods and systems would be easy to set up and use, unobtrusive and effective. Also ideally, such methods and systems would be suitable for use before, during and after a surgical procedure and would be acceptable to the patient while awake in the preoperative and postoperative settings. At least some of these objectives will be met by the embodiments described herein.